My daughter is very angry and therapy doesn't seem to be working

My family has been hurting a lot for the past 7 months. My oldest son took his life at the age of 15. That was the worst day of my life. My family is not and never will be the same. He overdosed on medication in the bathroom. He struggled with mental health and depression. I jad no idea it was that bad and I have to carry this guilt with me for the rest of my life.. My husband was the one who found him in the bathroom and he screamed for me, but my daughter, who's 11, beat me there. He picked her up because he didn't want her to see, but she saw. We called 911, but he was gone... There was no point... I was hoping they were gonna tell me there was still life in him. That there was still hope... But seeing his white face, I knew right away he was gone. When the paramedics got here and went up there, one of the ladies there looked at me and just said "Mama, I'm so sorry..." I just cried. I have never felt so worthless in my life that I couldn't save my son. I didn't even know my daughter was peaking out of her room. They took my sons body from me... We had his memorial and he's thank God for our neighbors. They set up a gofundme to help with a tombstone.

Over the last 7 months my daughter developed severe anger issues. She gets angry a lot quicker and will throw things, curse, say she hates us. She's in therapy but its not working because she refuses to talk. She is suspended from school because she threw her desk at her teacher. She hadn't finished writing down the homework and her teacher was scolding her. Her teacher said she rolled her eyes and this teacher, who had my son when he was in the 5th grade said to her "You really think your brother would be proud of this behavior." Mentioning her brother is a way to set her off and she got so mad she threw her desk at the teacher. I'm not excusing my daughters behavior but its barely been 7 months. I felt her comment was very insensitive. Her anger just seems to be getting worse and I dont know how to help her if she won't even talk to her therapist. I feel I dont even have time to grieve myself because I'm trying so hard to handle my daughter. And all anyone says is "It will get better." And I'm so tired if hearing that. It helps absolutely nothing